[Caldon]

I own factory built ERA #2058, a 289 FIA Street model with the drop down dash & typical SW street gauge layout. I've replaced the SW Amp gauge with a SW one showing Volts. All gauges and lights function as they should (finally), BUT, the last gremlin is when I flip the light toggle switch on to either of the two positions, the gas gauge "pegs" to the full position regardless of how much gas is actually in the tank. When the light toggle switch is moved to "off", the gas gauge returns to showing the current gas level. I suspect some sort of grounding short, but I don't see any connection between these two gauges in the wiring diagram. What am I missing? Any suggestions are appreciated.